Microsoft says “the update does increase the reliability, performance, and resiliency provided by Kernel Patch Protection.” The question is, why and what is really the problem for this high priority update? Allegedly there could be a vulnerability in the x64 kernel which is why this patch update may be so important. For example PatchGuard keeps 64-bit Vista safer from unsigned code so that when you install a driver from a 3rd party any malicious code does not affect the Kernel.